Unlike Jupiter's four large Galilean moons, which are visible from Earth with even small backyard telescopes, both new moons are dim and very distant from the planet, taking about 580 and 726 days to complete their orbits.

Scientists had previously discovered new Jovian satellites in 2010, and astronomers think there may be more—lots more.

"The satellites are part of the outer retrograde swarm of objects around Jupiter," said Scott Sheppard, of the Department of Terrestrial Magnetism at the Carnegie Institute for Science in Washington, D.C., who reported the discovery.

Retrograde satellites are moons that orbit "backward"—in the opposite direction of a planet's axial rotation. Including the two new moons, the Jupiter swarm features 52 known retrograde satellites, which are all relatively tiny.

"It is likely there are about a hundred satellites of this size" in the swarm, Sheppard said.